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L Mezger-Freed

Publications and source records attributed to L Mezger-Freed.

11 recordsLinked to original sources
PubMed1977

Chromosomal evolution in a haploid frog cell line: implications for the origin of karyotypic variants.

ICR 2A, a haploid cell line derived from Rana pipiens embryos, has remained haploid in number of chromosones and their relative lengths and centromere positions for 500 cell generations. After this time, two new haryotypes appeared; relative length measurements indicate that the first has a translocation from chromosome 4 to 6, the second translocations from 3 and 4 to 6 and 7. The single exchange karyotype is not a precursor for the double exchange according to a statistical analysis. The double exchange karyotype characterized 90% of some cultures although a selective advantage could not be demonstrated for these cells. The observations suggest that a non-clonal or multicellular origin may account for these karyotypic variants.

Animals↗
PubMed1975

Mutagenesis of haploid cultured frog cells.

Haploid cells afford an opportunity to test some of the assumptions from bacterial genetics which have been adopted by somatic cell geneticists. Haploid cultured cell lines derived from the grass frog Rana pipiens were compared to diploid cell lines in order to test a model which predicts that recessive mutations will be expressed in diploid cells with a frequency equal to the square of that in haploid cells. Haploid and diploid monolayer cultures were compared for (1) survival after exposure to compounds known to be mutagenic for bacteria (a measure of the frequency with which lethal mutations are expressed), and (2) the induction of drug-resistant variants (putative mutants) by such compounds. The proportion of cells which survived from diploid cultures was no more than ten times that from haploid cultures, a much smaller difference than predicted. Furthermore, the frequency of drug-resistant variants was independent of polidy. Therefore, the validity of the following assumptions is in question: (1) Haploid eukaryotic cells express mutations with a frequency comparable to that in bacteria; (2) molecules which increase the frequency of stable phenotypic variants in culture do so by inducing gene mutations; (3) stable phenotypic variants whose frequency in culture is increased by putative mutagens arise as the result of gene mutation.

Acridines↗
PubMed1974

An analysis of survival in haploid and diploid cell cultures after exposure to ICR acridine half-mustard compounds mutagenic for bacteria.

Population changes induced by acridine mustards in haploid and diploid cultured cell lines from Rana pipiens were compared to test the expectation that recessive mutations will be expressed in diploid cells with a frequency equal to the square of that in haploid cells, and to investigate the usefulness of such comparison for the screening of possible mutagens. The differences in survival frequency after treatment were much smaller than predicted on the basis of the expression of lethal (recessive) mutations alone. Survival was also affected by culture conditions, drug-resistance phenomena, and other cell properties. It is suggested that with the evolution of epigenetic processes for the production of stable phenotypes, the vertebrate cell also acquired more efficient means to prevent the expression of gene mutation and that the acridine compounds may affect both epigenetic and genetic changes.

Acridines↗
PubMed1971

Puromycin resistance in haploid and heteroploid frog cells: gene or membrane determined?

The frequency of colony formation in monolayers of cultured frog cell lines treated with puromycin was compared in (a) haploid and heteroploid lines and (b) mutagen-treated and nontreated haploid lines. Evidence that resistant colonies result from gene mutation was negative, since the colony frequency is independent of both ploidy and mutagen treatment. A study of five frog cell lines showed that colony formation in puromycin depends on (a) the concentration of puromycin, (b) preselection of the population with puromycin, and, particularly, (c) the capacity of the treated population to survive some exposure to puromycin. One haploid and one heteroploid strain showing stable resistance to puromycin have been isolated; comparison of those variants with sensitive populations has shown that resistance to puromycin is correlated with the cells' capacity to exclude the drug. The evidence for different levels of membrane permeability, combined with evidence for many degrees of resistance among and within cell populations, suggests a model of self-determining membrane units. The evolution of a resistant phenotype may result from changes in the proportion of specific units in the membrane population.

Animals↗
PubMed1970

Stable haploid cultured cell lines from frog embryos.

Two haploid cell lines have been established from androgenetic embryos of the frog, Rana pipiens; one line has been maintained in culture for 150 generations, the other for 200 generations. Karyotypes of the two lines agree well with the standard for the species although some chromosomes show small differences in length. The cells multiply in the same defined basal medium used for culture of other anuran cell lines; this medium consists of the usual amino acids, vitamins, and serum macromolecules plus an exogenous purine source. Both the haploids resemble "permanent" cell lines in their prolonged multiplication in culture. The two lines differ in their mode of growth, one being epithelial-like, the other forming an overlapping meshwork of fibroblast-like cells. Both have the low plating efficiency characteristic of "unaltered" cells. These two lines are exceptional in their ability to compete successfully with the diploid variants which arise by endomitosis or cell fusion and which usually overgrow the haploid population. The more vigorous line, RPH 68.2A, should provide the long-desired haploid material for genetic studies in cell culture.

Animals↗